Structural components for marine outboard engines, including driveshaft spacers, have historically been cast using high-pressure die casting or sand casting. These casting processes result in a number of deficiencies when preparing structural components for marine outboard engines.
Casting introduces excessive weight. Casting requires the use of draft angles so that the component may be extracted from the die following casting. As a result, components comprising draft angles incorporate an excess of metal that, in turn, incorporates unnecessary weight into the component.
Cast components are prone to cosmetic defects. Cast components have high porosity and/or are covered in die lubricants, either of which may lead to subsequent cosmetic defects in the final part. To ameliorate cosmetic defects, cast components may also be de-gated or ground on coarse sanding belts to remove some or all or the as-cast surface. Post-casting processing, however, requires additional steps and injects increased cost into the manufacturing process as well as creating additional cosmetic issues.
Cast components also generally have a limited ability to absorb impact energy. Even the best cast aluminum alloys have decreased tensile ductility compared to a wrought alloy. As a result, the components prepared by casting have limited ability to absorb impact energy. Further exacerbating this problem is that the incorporation of design features intended to deform to mitigate impact events are minimally effective because of low tensile ductility of cast alloys.
Protective barrier coatings are difficult to apply. Traditional cast alloys have high silicon content. This results in the production of components that are more difficult to anodize and/or conversion coat compared to wrought alloys.
Casting requires expensive upfront tooling costs. Casting dies are expensive to produce, require long lead times to design and manufacture, and need maintenance over their effective lifetimes. Moreover, casting dies are incapable of being used for components of different sizes or lengths. This necessitates that the design and manufacture of different casting dies for each individualized component.
As a result, there is a need for structural components for a marine outboard engine that are not prepared by casting processes or that comprise casting alloys.